Column-oriented NoSQL databases espouses a model where data in stored in a column-oriented way. This contrasts with the row-oriented format in RDBMS. The column-oriented storage allows data to be stored effectively. It avoids consuming space when storing nulls by simply not storing a column when a value doesn’t exist for that column. Each unit of data can be thought of as a set of key/value pairs, where the unit itself is identified with the help of a primary identifier, often referred to as the primary key or Row-Key.Also units are stored in an ordered-sorted manner. The units of data are sorted and ordered on the basis of the row-key.
Column family databases are still extremely scalable but less-so than key-value stores. However, they work better with more complex data sets.
Examples of Column family databases are: Apache HBase,Hypertable,Cassandra, Google’s Bigtable etc.
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